The present invention relates to a dryer header system incorporating a web guide, typically for use in web flotation drying applications.
Conventional air bars and air duct delivery systems are designed to obtain even air flow to the web occurs notwithstanding minor disturbances in duct delivery systems. Uneven air distribution is generally considered to be undesirable, since the same can result in drying streaks on the web, improper clearance of the web from the air bar surface, and/or improper flotation of the web (e.g., web flutter). Thus, in a conventional air bar having more than one air receiving port in communication with a duct delivery system, if one port is supplied air at a pressure different from that at which another port is supplied air, the air bar is designed so that the two different air supplies mix in an internal chamber of the air bar, allowing even pressure air delivery to the web.
In addition, as a floating web approaches the edge of an air bar, the pressure pad which allows web flotation collapses, causing web flutter. This phenomenon is similar to the edge of an unattached sail on a sail boat, and in flotation drying, is undesirable. Accordingly, webs are typically positioned about 1-4 inches from the air bar edges.
It would, however, be desirable to continuously control or compensate for web shift occuring during the drying operation, regardless of the cause thereof. It is therefore an object of the present invention to compensate for such web shift.
It is a further object of the present invention to provide apparatus to control the pressure differential between two ducts feeding a given air bar.